Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

hello monks,

I want to comapre 2 strings and extract the longest common substring based on words.

I have used 

my $seg1 = "The man who likes reading books and writing poems."
<p>my $seg1 = "The man who likes reading big books and poems."

<p>lcss( "$seg1", "$seg2" );

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but the result is based on strings. The output is:

The man who likes reading b

Is any algorithm in perl that returns

The man who likes reading?

I would be also happy having sommethins like:

The man who likes reading * * * poems

Replies are listed 'Best First'.
Re: Find substring based on words and not in charachters
by Corion (Patriarch) on Dec 02, 2014 at 16:14 UTC

    You can feed Algorithm::Diff words instead of lines and it will return you the longest common subsequence through the LCS function.

[reply]
[d/l]
Re: Find substring based on words and not in charachters (Updated.)
by BrowserUk (Patriarch) on Dec 02, 2014 at 17:06 UTC

    Update: Added minor optimisation. Update2: Rolled the optimisation into the while loop.

    Something like this?:

    #! perl -slw
use strict;

my $seg1 = "The man who likes reading books and writing poems.";
my $seg2 = "The man who likes reading big books and poems.";

my $best = '';
while( length( $seg1 ) > length( $best ) ) {
    while( $seg1 =~ m[(?!\s)(?=(\b.+\b)(?!\s))]g ) {
        my $bit = $1;
        $best = $bit if $seg2 =~ m[\Q$bit] and length( $bit ) > length
+( $best );
    }
    $seg1 =~ s[(?:\s|^)\S+$][];
}
print $best;

__END__
[17:04:21.46] C:\test>junk39
The man who likes reading

    [download]
    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
      I'd compare word count instead of length.
      لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
[reply]

        The OP certainly could go that way, but I see two problems with it:

        1. Deciding upon a definition for a "word".
        2. Are a few short words more meaningful than 1 less long one?

          Eg. "on the way to" -v- "the Riechstag Bureau"?

        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

        OP states he is looking for longest string; he wants to avoid getting parts of words, such as the last 'b' the lcss algorithm finds.

        1 Peter 4:10
[reply]

      Hi,

      Thanks a lot for your code! It works perfect :)

[reply]

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